dirs: Don't ship channels directory

Starting with libvirt 9.7.0, channels are created under
/run/libvirt instead of /var/lib/libvirt, so we no longer need
to ship any directory as part of the package.

The migration between the two locations happens seamlessly:
domains that are running when the upgrade is performed keep
using the old directory, while domains that are started
afterwards use the new one.

As a result of that, if there are any running domains during
the upgrade, dpkg will refuse to delete the old directories.
Add a postint snippet that will take care of cleaning up
during a future upgrade, once all domains have been restarted
and are thus using the new location.

debian/libvirt-daemon-system.dirs

@@ -8,7 +8,6 @@ var/cache/libvirt/qemu
 var/lib/libvirt/boot
 var/lib/libvirt/images
 var/lib/libvirt/qemu
-var/lib/libvirt/qemu/channel/target
 var/lib/libvirt/sanlock
 var/log/libvirt/lxc
 var/log/libvirt/qemu

debian/libvirt-daemon-system.postinst

@@ -74,8 +74,6 @@ add_statoverrides()
 
     QEMU_DIRS="
         /var/lib/libvirt/qemu/
-        /var/lib/libvirt/qemu/channel/
-        /var/lib/libvirt/qemu/channel/target/
     "
 
     SANLOCK_DIR="/var/lib/libvirt/sanlock"
@@ -124,6 +122,14 @@ case "$1" in
             rmdir --ignore-fail-on-non-empty /var/log/libvirt/uml
         fi
 
+        # Directories used for channels until 9.7.0-1
+        if [ -d /var/lib/libvirt/qemu/channel/target ]; then
+            rmdir --ignore-fail-on-non-empty /var/lib/libvirt/qemu/channel/target
+        fi
+        if [ -d /var/lib/libvirt/qemu/channel ]; then
+            rmdir --ignore-fail-on-non-empty /var/lib/libvirt/qemu/channel
+        fi
+
         # Force refresh of capabilities (#731815)
         rm -f /var/cache/libvirt/qemu/capabilities/*.xml